The present invention relates to a high-frequency snare for an endoscope, which is inserted in a forceps channel of the endoscope and used for endoscopic excision of mucous membrane, and a method of forming such a high-frequency snare.
The high-frequency snare for the endoscope is typically formed such that a plurality of resilient metal wires are connected at their proximal and distal ends, to form a loop. When the connected wires are withdrawn inside a sheath, which has electrically insulating property, the wires resiliently deform and the loop is tucked, while when the wires are protruded from the sheath, the loop expand its full state due to the resilient property of the wires.
If a single line metallic wire is used for each of the plurality of wires forming the high-frequency snare, the resiliency may be too strong and may cause a problem when in use. Therefore, typically, as each wire for the snare, a twisted wire consisting of a plurality of thin wires which are twisted to form a single line of wire is used. At each end, the plurality of thin wires are connected by silver brazing, laser welding or plasma welding. Examples of such configurations are disclosed in Japanese Patent Provisional Publication No. P2000-83963A and Japanese Patent Publication No. H5-54343.
The high-frequency snare for the endoscope is typically used for tightly binding a polyp and cut it out by applying a high-frequency current to the snare. Recently, however, as an endoscopic mucous membrane excision is performed. In such a case, by use of a tip connected portion of the resilient wires, which portion is protruded frontward from the tip of the loop, the excision of the mucous membrane and detachment of the cut portion are performed, which have not yet been done before.
That is, the connecting portion of the wires that form the loop is used as the high-frequency electrode. By slightly inserting the connection portion in the mucous membrane and supplying a high-frequency current thereto, a portion where the connection portion of the resilient wires and the mucous surface is cauterized. Therefore, by moving the resilient wire with maintaining the above condition, the excision of the mucous membrane can be done.
When the mucous detachment is performed, the portion of the mucous which has been cut out by the excision operation is detached from the muscular layer, the connection portion of the resilient wires is inserted between the bottom side of the mucous membrane and the muscular layer. Then, the cut portion of the mucous membrane is removed with the high-frequency current being supplied to cut the tissues between the mucous membrane and the muscular layer.
When the high-frequency snare is used in the above way, however, electric sparks are generated between the connected portion of the resilient wires which serve as the high-frequency electrodes and the mucous membrane, and the temperature at that portion raises significantly.
If the wires are connected, at the connected portion, by silver brazing, the silver braze may be softened by the generated heat, and some of the wires may be disconnected, thereby breaking the snare loop.
If the wires are connected, at the connected portion, by the laser welding or the plasma welding, a very high temperature is applied to the wires when welded and the connected portion may become very brittle. Accordingly, if concentrated stress is generated when the mucous membrane is detached, the snare loop may easily be broken.
In addition, in the case of the laser welding or plasma welding, if the resilient wire consists of a single wire, the resilient wire is damaged little, while the wire is a twisted wire, relatively large damage is applied to the twisted wire as each wire segment has heated to a high temperature and it is difficult to carry out the welding operation.